The present invention relates generally to keratinocyte growth factor (xe2x80x9cKGFxe2x80x9d). More specifically, this invention relates to a KGF fragment and analogs thereof having increased biological activity, and decreased cytotoxicity as compared to a mature, at recombinant, full length KGF expressed in an insect cell expression system. This KGF fragment lacks the first 23 amino acid residues of the N-terminus of mature, full-length KGF, including a potential glycosylation site. The N-terminus was previously believed to confer upon KGF its epithelial cell specificity.
KGF belongs to the family of fibroblast growth factors (xe2x80x9cFGFsxe2x80x9d), the prototype of which is represented by basic FGF (xe2x80x9cbFGFxe2x80x9d). KGF is, hence, also known as FGF-7. Like other FGFs, KGF is a heparin-binding protein, but unlike other FGFs, it has a unique target cell specificity. In particular, FGFs are generally capable of stimulating the proliferation and differentiation of a variety of cell types derived from the primary or secondary mesoderm as well as from neuroectoderm. KGF is similar to other FGFs in its ability to stimulate epithelial cell proliferation, but is dissimilar to other FGFs in its inability to stimulate endothelial cells or fibroblast proliferation, as discussed in Finch, P. W. et al., Science 245: 752-755 (1989). Mature, full-length KGF, designated herein as KGF163, is a polypeptide with 163 amino acid residues, and possesses a potential N-glycosylation site at amino acid 14 of the consensus sequence for glycosylation that extends from amino acid residue 14 to 16 at the N-terminus, as indicated in Finch et al. (1989), loc. cit.
FGFs, including acidic fibroblast growth factor (xe2x80x9caFGFxe2x80x9d) and basic fibroblast growth factor (xe2x80x9cbFGFxe2x80x9d), are known to have heparin-binding properties and have the ability to induce the differentiation and proliferation of ventral, as well as dorsal, mesoderm in early blastulae, as discussed in Gospodarowicz et al., Cell. Biol. Rev. 25:307-314 (1991), and Basilico et al., Adv. Cancer Res. 59:115-165 (1992). The response of cells to FGF is mediated through binding thereof to cell surface receptors known as fibroblast growth factor receptors (xe2x80x9cFGFRsxe2x80x9d), of which there are three inter-related types, as discussed in Hou et al., Science 251:665-668 (1991). High affinity FGFRs are tyrosine kinases and include the flg receptor (xe2x80x9cFGFR-1xe2x80x9d), the bek receptor (xe2x80x9cFGFR-2xe2x80x9d), and the K Sam receptor (xe2x80x9cFGFR-3xe2x80x9d), as discussed in Lee et al., Science 245:57-60 (1989); Dionne et al., EMBO J. 9:2685-2692 (1990); Miki et al., Science 251:72-75 (1991); Miki et al., Proc. Natl. Acad. Sci. USA 89:246-250 (1992); and Dell et al., J. Biol. Chem. 267:21225-21229, (1992).
Both FGFR-1 and FGFR-2 are widely expressed in mesodermal and neuroectodermal tissues, and both are able to bind aFGF and bFGF with similar affinities. FGFR-3, also referred to as KGFR, is a KGF receptor that is specific to epithelial cells. It is an alternative transcript of FGFR-2. In contrast to FGFR-2, which shows high affinity for both AFGF and bFGF and no affinity for KGF, FGFR-3 binds KGF and AFGF with an affinity approximately 20 to 1000 fold higher than bFGF, as discussed in Miki et al. (1992), and Dell et al. (1992), loc. cit.
The tightly restricted tissue distribution of KGFR to epithelial cells and, therefore, the tissue restricted activity of KGF, is desirable in many types of wound healing applications, as well as in the treatment of hyperproliferative diseases of the epidermis, such as psoriasis and basal cell carcinoma. Presently, except for KGF, no highly suitable factor exists for these applications. It would be desirable, therefore, if KGF could be modified to increase its potency and decrease its cytotoxicity for therapeutic applications.
Recently, Ron et al., J. Biol. Chem. 268:2984-2988 (February 1993) found that when KGF163, was expressed in a prokaryotic expression system, a recombinant KGF (xe2x80x9crKGFxe2x80x9d) polypeptide could be obtained that possessed mitogenic activity. When the rKGF molecule was truncated by deletion of 3, 8, 27, 38, and 48 amino acid residues from the N-terminus of the mature KGF163 polypeptide, biological activity of the resulting molecules varied. With deletion of 3 and 8 amino acid residues, respectively, the mitogenic activity of the resulting molecules did not appear to be affected as compared to full-length rKGF. Deletion of 27 amino acid residues, however, resulted in molecules that display 10-20 fold reduced mitogenic activity. Deletion of 38 and 48 amino acid residues, respectively, resulted in complete loss of mitogenic activity and heparin-binding ability. Ron et al., however, failed to produce any truncated rKGF fragments that possessed increased mitogenic activity as compared to the full-length rKGF molecule.
One of the objects of the present invention is to provide a KGF fragment or an analog thereof that contains a portion of the amino acid sequence of mature, full-length KGF and that exhibits at least a 2-fold, but preferably 7-fold, more preferably, a 7-10 fold increase in mitogenic activity as compared to the mature, full-length rKGF. This KGF fragment lacks a sequence comprising the first 23 N-terminal amino acid residues, C-N-D-M-T-P-E-Q-M-A-T-N-V-N-C-S-S-P-E-R-H-T-R- (SEQ ID NO: 2), of the mature, full-length rKGF.
Another one of the objects of the present invention is to provide a KGF fragment, as above, that has decreased cytotoxicity as compared to the mature, full-length rKGF.
Still another one of the objects of the present invention is to provide a conjugate that comprises the KGF fragment described above and a toxin molecule. The toxin molecule can be one of a ricin A molecule, a diphtheria toxin molecule, or a saporin molecule.
Yet another one of the objects of the present invention is to provide a therapeutic composition that contains the KGF fragment as described above and a pharmaceutically acceptable carrier, for example, one suitable for topical application to human skin.
Still another one of the objects of the present invention is to provide a DNA molecule that is composed of a nucleotide sequence that encodes the KGF fragment described above.
Yet another one of the objects of the present invention is to provide an expression vector that contains the DNA molecule that encodes the KGF fragment above and a regulatory sequence for expression of the DNA molecule. The expression vector can be, for example, a yeast, a bacterial, a mammalian or a baculovirus expression vector.
Yet another one of the objects of the present invention is to provide a host cell transformed with the expression vector described above. The host cell can be, for example, a prokaryote such as a bacterial cell, or a eukaryote such as a yeast cell, a mammalian cell, or an insect cell.
Yet another one of the objects of the present invention is to provide a method of producing the KGF fragment by culturing the transformed host cell as described above and isolating the KGF fragment from the culture.
Still another one of the objects of the present invention is to provide a method of stimulating epithelial cell growth by applying the KGF fragment to an area in which epithelial cell growth is desired and allowing the cells to grow.
Still another one of the objects of the present invention is to provide a method for wound healing by applying the therapeutic composition described above to an area of a wound to be treated and allowing the wound to heal.
Still another one of the objects of the present invention is to provide a method of treating a hyperproliferative disease of the epidermis by applying the conjugate described above to an area to be treated.
Further objects, features, and advantages of the present invention would be apparent to a person of ordinary skill in the art and need not be enumerated here.